This invention relates to an improved process for producing amine formaldehyde resin foam, characterized by using an organic compound having a low boiling point, and particularly relates to a process for producing amine formaldehyde resin foam having good mold-filling property, uniform cell structure and low density and which is easily dried.
Amine formaldehyde resin foam is cheap, makes an excellent heat shield, absorbs sound and is self-extinguishing. The resin foam is utilized as a heat insulating material for housing, a heat insulating material for low temperature storage, a sound insulating material, and decorative material. Amine formaldehyde resin foam having water absorbing property is used for agriculture.
Organic foams are being used in a variety of fields, and their production increases annually. Therefore, it is necessary that the organic foams have fire resistance and be easily disposed as a waste material.
Amine formaldehyde resin foams are self extinguishing and are biologically degradable. So, the resin foams satisfy the requirements as mentioned above.
Many processes for producing amine formaldehyde resin foam are well known. However, the only process carried out on a commercial scale is the process comprising mixing an aqueous solution of a precondensate for urea resin with an aqueous solution of a foaming agent and a curing agent while blowing air into the solution to foam the mixture, and curing the foam. However, in effecting the foaming-operation according to this process, the weight of the water used is 3 to 6 times that of the solid content of the precondensate, so the resulting foam contains a large amount of water. The water must be removed from the foam through drying, and it takes 4 to 7 days to remove such water from the foam through natural drying. This is a disadvantage in using the foam in housing.
Two processes for producing amine formaldehyde resin foam using an organic compound having a low boiling point are known in the art: one comprises mixing an aqueous precondensate for the resin solution, a foaming agent and a surfactant at a temperature less than the boiling point of the foaming agent and emulsifying the mixture and adding a curing agent to the mixture and then charging the mixture into a mold and foaming it by heating it at a temperature above the boiling point of the foaming agent. The other comprises foaming a highly viscous precondensate for the resin by vaporizing a foaming agent through heat of neutralization. [Refer to Japanese Patent Publication (Kokai) No. 40669/1975)]
In the former process, good foam can be obtained only when the foaming and curing operations have been effected very slowly. The foaming operation takes a long time. The emulsification is difficult in case of using a foaming agent having a low boiling point, and much foaming agent is lost.
In the latter process, an excess of an acid and a base is required. The salt obtained through neutralization has anti-foaming action and the acid catalyst employed not only promotes curing reaction, but also participates in the neutralization reaction. So, it is difficult to decide how much acid to use.
The above shortcomings in the processes for producing amine formaldehyde resin foam are derived from the following properties of the amine formaldehyde resin:
(1) The precondensate for amine formaldehyde resin is hydrophilic and is incompatible with a foaming agent composed of an organic compound having a low boiling point, the precondensate and the foaming agent are hard to mix with each other.
(2) The curing reaction of the amine formaldehyde resin is slow. So, it is difficult to maintain good balance between foaming and curing, and degassing of the foaming agent is likely to occur.
(3) The precondensate for amine formaldehyde resin generates little heat when being cured. The precondensate causes curing reaction as well as decomposing reaction at a high temperature.